Structural Detailing of Reinforcement for Economy - Simplified Design of Reinforced Concrete Buildings - page 254

(3) Lap Splice Length

The load combination represented by point 8 (ACI Eq. (9-6)) in Fig. 8-11 governs the type of lap splice
to be used, since it is the combination that produces the greatest tensile stress f s in the bars. Note that
the load combination represented by point 6 (ACI Eq. (9-4)) which governed the design of the column
does not govern the design of the splice. Since 0 < f s < 0.5 f y at point 8, a Class B splice must be used
(all the bars spliced ACI 12.17.2.2).

Required splice length = 1.3 ˜ d where ˜ d is the tension development length of the No.10 bars (of the
lower column).

Clear bar spacing 3.5 in. = 2.8 d b (see Fig. 8-2)

Cover > d b = 1.27 in.

From Table 8-1, ˜ d = 60.2 in.

1.3˜ d = 1.3 60.2 = 78.3 in.

Thus, a 6 ft-6 in. splice length would be required which is more than one-half of the clear story height.

Decreasing the bar size in the 1st story columns would result in slightly smaller splice lengths; how-
ever, the reinforcement ratio would increase from 4% (8-No.10) to 4.7% (12-No.9). Also, labor costs
would increase since more bars would have to be placed and spliced.

One possible alternative would be to increase the column size. For example, a 18 18 in. column
would require about 8-No.8 bars in the 1st story. It is important to note that changing the dimensions
of the columns would change the results from the lateral load analysis, affecting all subsequent calcu-
lations; a small change, however, should not significantly alter the results.

References

8.1 ACI Detailing Manual - 2004, SP-66(04), American Concrete Institute, Farmington Hills, Michigan, 2004,
(PCA LT185).

8.2 Stecich, J.P., Hanson, J.M., and Rice, P.F., “Bending and Straightening of Grade 60 Reinforcing Bars,”
Concrete International: Design & Construction, VOl. 6, No. 8, August 1984, pp. 14-23.

8.3 “Suggested Project Specifications Provisions for Epoxy-Coated Reinforcing Bars,” Engineering Data
Report No. 19, Concrete Reinforcing Steel Institute, Schaumburg, Illinois, 1984.

8.4 Types of Mechanical Splices of Reinforcing Bars, ACI Committee 439, American Concrete Institute,
Farmington Hills, Michigan, 2007, 22 pp.